GRAVITY-INDUCED FORMATION OF CONCENTRATION GRADIENTS IN SUPERSATURATED BINARY-SOLUTIONS

Experimental and theoretical studies of the formation of solute concen tration gradient in supersaturated binary solutions in a gravitational held were carried out. The formation of solute concentration gradient was associated with the gravity induced redistribution of subcritical solute clusters. The birth-death process of the new solute-rich phase domains (subcritical solute clusters) was described in terms of the t ime-dependent Ginzburg-Landau model developed for metastable state rel axation in binary (solute + solvent) non-critical solutions in the pre sence of a gravitational held. A new mathematical Ansatz was developed for solution of the model equations. This Ansatz has allowed to appro ach for the first time the following important problems: (A) Microstru cture of solute distribution inside of the subcritical solute clusters . The analytical results obtained demonstrate that solute inside of th e subcritical solute clusters is heterogeneously distributed with a sp atially periodic structure. (B) Macrostructure of the solute subcritic al clusters distribution in a gravitational field. The subcritical sol ute clusters are found to be distributed heterogeneously in a gravitat ional held. This heterogeneity, which is due to the heterogeneous birt h-death process of the subcritical solute clusters in a gravitational held, initiates a noticeable solute concentration gradient in vertical columns of supersaturated binary solutions. An analysis and compariso n of theoretical results and experimental data related to the solute c oncentration gradient formation in a gravitational field are presented . It is also demonstrated that the critical radius of solute clusters (radius of nucleation) and induction time are gravity-dependent.